The present invention relates to refrigerant expansion valves of the type typically operated by a thermally responsive sensor such as a fluid filled capsule and which employ in combination an electrically operated shutoff valve at the inlet of the expansion valve. Valves of this type have found applications in motor vehicle passenger compartment air conditioning systems where high ambient thermal loads are encountered and rapid changes in refrigerant flow are often required to maintain passenger comfort.
Heretofore, such combination thermally operated expansion valves with an electrically operated inlet shutoff valve have experienced problems where the electrically operated inlet shutoff valve included a solenoid actuator. Valves of this type have encountered unacceptable levels of noise upon energization of the inlet valve. This noise has been attributed to the solenoid armature reaching a sufficient velocity to generate audible noise when the armature reached the end of its travel by closing a working air gap.
Furthermore, where such valves are pilot operated, upon opening of the main valve the velocity of the fluid flowing past the pilot valve opening creates an aspiration effect generating a reduced pressure through the pilot passage and the pilot chamber on the distal end of the pilot passage. The reduced pressure in the pilot chamber has resulted in sticking of the armature in the open position and failure of the valve to close upon de-energization of the solenoid even under the urging of a return spring.
Thus, it has been desired to provide a way or means of reducing the opening noise of a solenoid operated shutoff valve at the inlet of a refrigerant expansion valve and to prevent sticking of the solenoid armature in the open position upon energization of the valve and flow of refrigerant through the valve. It has further been desired to provide a valve without opening noise, which is resistant to sticking upon electrical energization of the solenoid and which is low in manufacturing cost and easy to assemble so as to be competitive in high volume mass production for automotive air conditioning system applications.
The present invention provides a refrigerant expansion valve with a body having an inlet and outlet with an expansion valve member disposed in the flow path between the inlet and the outlet. Movement of the expansion valve member is effected by an operating member or rod adapted for attachment to a thermal actuator in a manner well known in the art. The valve body has attached thereto a solenoid operated inlet shutoff valve with a valve seat disposed in the flow path between the expansion valve and the inlet. An inlet valve member is disposed on the inlet valve seat and connected to the armature of the solenoid operator for effecting movement of the inlet valve member upon energization of the solenoid. In the preferred embodiment, the inlet valve member includes a pilot passage and pilot valve member disposed within the armature.
The armature is slidably moveable in a pressure-sealed armature guide preferably having a pole piece at the end thereof remote from the pilot valve and the armature defines a working air gap with the pole piece. A resilient limit stop is provided on the pole piece to cushion the deceleration of the armature and limit the closing of the working air gap to prevent noise and armature sticking.
A cross port is provided in the armature to alleviate the problem of reduced pressure on the distal end of the armature caused by aspiration during flow past the pilot passage.